CVE-2021-41862
📋 TL;DR
CVE-2021-41862 is a critical remote code execution vulnerability in AviatorScript that allows attackers to execute arbitrary code by crafting malicious expressions encoded with BCEL. This affects all applications using vulnerable versions of AviatorScript for expression evaluation. Attackers can achieve full system compromise if the application processes untrusted input.
💻 Affected Systems
- AviatorScript
📦 What is this software?
Aviatorscript by Aviatorscript Project
⚠️ Risk & Real-World Impact
Worst Case
Complete system takeover with attacker gaining full control over the server, data exfiltration, lateral movement, and persistent backdoor installation.
Likely Case
Remote code execution leading to application compromise, data theft, and potential ransomware deployment.
If Mitigated
Limited impact if proper input validation and sandboxing are implemented, though exploitation may still be possible.
🎯 Exploit Status
Exploitation is straightforward with publicly available proof-of-concept code. Attackers only need to craft a malicious expression payload.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.3.0 and later
Vendor Advisory: https://github.com/killme2008/aviatorscript/issues/421
Restart Required: Yes
Instructions:
1. Update AviatorScript dependency to version 5.3.0 or later. 2. Update pom.xml or build.gradle with new version. 3. Rebuild and redeploy application. 4. Restart all affected services.
🔧 Temporary Workarounds
Input Validation and Sanitization
allImplement strict input validation to reject any expressions containing BCEL encoding or suspicious patterns.
Sandbox Execution
allRun AviatorScript in a restricted security manager context with minimal permissions.
🧯 If You Can't Patch
- Implement network segmentation to isolate vulnerable applications from critical systems.
- Deploy web application firewall (WAF) rules to block BCEL-encoded payloads and expression injection attempts.
🔍 How to Verify
Check if Vulnerable:
Check your project's dependency management file (pom.xml, build.gradle) for AviatorScript version <=5.2.7.Check Version:
mvn dependency:tree | grep aviatorscript OR gradle dependencies | grep aviatorscriptVerify Fix Applied:
Verify AviatorScript version is 5.3.0 or higher in your dependencies and test expression evaluation with known safe inputs.📡 Detection & Monitoring
Log Indicators:
- Unusual expression evaluation errors
- Java class loading from unexpected sources
- BCEL-related class names in stack traces
Network Indicators:
- HTTP requests containing BCEL-encoded payloads
- Unusual outbound connections from application servers
SIEM Query:
source="application.logs" AND ("BCEL" OR "com.sun.org.apache.bcel" OR "ExpressionEngineException")